An experimental investigation of steam ejector refrigeration system powered by extra low temperature heat source

A steam ejector refrigeration system is a low capital cost solution for utilizing industrial waste heat or solar energy. When the heat source temperature is lower than 80 °C, the utilization of the thermal energy from such a low-temperature heat source can be a considerable challenge. In this investigation, an experimental prototype for the steam ejector refrigeration system was designed and manufactured, which can operate using extra low-temperature heat source below 80 °C. The effects of the operation temperature, the nozzle exit position (NXP) and the diameter of the constant area section on the working performance of the steam ejector were investigated at generating temperatures ranging from 40 °C to 70 °C. Three ejectors with a same de Laval nozzle for the primary nozzle and three different constant-area sections were designed and fabricated. The experimental results show that a steam ejector can function for a certain configuration size of the steam ejector with a generating temperature ranging from 40 °C to 70 °C and an evaporating temperature of 10 °C. For a given NXP, the system COP and cooling capacity of the steam ejector decreased until inoperative as the diameter of the constant area section reduced. The results of this investigation provided a good solution for the refrigeration application of the steam ejector refrigeration system powered by an extra low-temperature heat source.     

Optimisation of hybrid cane-based combined heat and power-concentrating solar thermal power plants of 30 MW

The benchmarking and optimal power extraction from a cane-based combined heat and power (CHP) plant using state-of-the-art processes has been underestimated. This study indicates that the export power potential can be much more than the presently achieved values of 5.8–7.0 MW/1000 tcd (tonnes crushing per day). It can be 11–12 MW/1000 tcd. By integration of cane-based CHP with concentrating solar thermal (CST) – parabolic trough concentrators (PTC) systems of even size, the heat rate (power only) can be decreased from 2984.12 to 2088.89 kcal/kWh and the overall efficiency (power +heat) of 48.59% can be enhanced to 69.41%. The CHP potential of sugar mills will be considerable enhanced to 12 MW/1000 tcd by four elements: (a) integration with solar-concentrating collectors, (b) the use of high-efficiency, high-pressure boilers (>11.0 MPa and 560°C), (c) three-dimensional designed stage optimised steam turbines with high isentropic efficiencies of 92–94+% and (d) minimising in-house steam demand to below 225 kg/t of cane (=9.37 t/h per 1000 tcd) and in-house electric demand to below 22 kWh/t of cane (=0.91 MW/1000 tcd). Auxiliary power must be below 8% of the power export. Matching policy incentives will help in new initiatives and quick take off of new projects. The estimated potential for India for cane-based CHP is around 7 GW without solar systems and is 10 GW for hybrid CST–PTC cane-based systems. This is a zero fossil fuel-consuming technology.     

Process simulation of hydrogen production by steam reforming of diluted bioethanol solutions: Effect of operating parameters on electrical and thermal cogeneration by using fuel cells

The possibility to exploit diluted bioethanol streams is discussed for hydrogen production by steam reforming. An integrated unit constituted by a steam reformer, a hydrogen purification section with high- and low-temperature water gas shift, a methanator reactor and a fuel cell were simulated to achieve residential size cogeneration of 5 kW electrical power + 5 kW thermal power as target output.Process simulation allowed to investigate the effect of the reformer temperature, of bioethanol concentration and of catalyst loading on the temperature and concentration profiles in the steam reformer. The net power output was also calculated on the basis of 27 different operating conditions.P_electrical output ranging from 3.3 to 6.0 kW were obtained, whereas the total heat output P_{thermal, total} ranged from 3.9 to 7.2 kW. The highest overall energy output corresponded to P_electrical = 4.8 kW, P_{Thermal, FC} = 3.1 kW, P_{heat recovery} = 4.1 kW, for a total 12 kW energy output. This was achieved by feeding a mixture with water/ethanol ratio = 11 (mol/mol), irrespectively of the catalyst mass, and setting the ref split temperature so to have an average temperature of 635 °C in the ESR reactor.     

A solid state thermogalvanic cell harvesting low-grade thermal energy

A high performance polymer electrolyte thermogalvanic cell, which converts thermal energy to electrical energy directly, is transformed from a proton exchange membrane fuel cell. The transform is realized by connecting the anode and cathode chamber with a gas tube and filling hydrogen to both chambers. Provided a heat flux through the cell, hydrogen is consumed in the cold side and regenerated in the hot side while circulating in two chambers during operation. The Seebeck coefficient is 0.531 mV K^?1 at a cold side temperature of 60.0 °C and the maximum power density could reach up to 20 μW cm^?2 with a temperature difference of 15.3 °C between two electrodes.     

Four different configurations of a 5 kW class shell-and-tube methane steam reformer with a low-temperature heat source

The methane steam reforming reaction is an extremely high endothermic reaction that needs a high temperature heat source. Various fuel cell hybrid systems have been developed to improve the thermal efficiency of the entire system. This paper presents a low temperature steam reformer for those hybrid systems to maximize the utilization of energy from a low temperature waste heat source. In this study, the steam reformer has a shell and tube configuration that is divided into the following zones: the inlet heat exchanging zone, the reforming zone and the exit heat exchanging zone. Four different configurations for methane steam reformers are developed to examine the effect of heat transfer on the methane conversion performance of the low temperature steam reformer. The experimental results show that the overall heat transfer area is a critical parameter in achieving a high methane conversion rate. When the heat transfer area increases about 30%, the results showed elevated dry mole fractions of hydrogen about 3% with about 30 °C rise of reformer outlet temperature.     

Multi-Objective Optimization of Micro Pin-Fin Arrays for Cooling of High Heat Flux Electronics with a Hot Spot

ABSTRACT

This article presents fully three-dimensional conjugate heat transfer analysis and a multi-objective, constrained optimization to find sizes of pin-fins, inlet water pressure, and average speed for arrays of micro pin-fins used in the forced convection cooling of an integrated circuit with a uniformly heated 4 × 3 mm footprint and a centrally located 0.5 × 0.5 mm hot spot. Sizes of micro pin-fins having cross sections shaped as circles, symmetric airfoils, and symmetric convex lenses are optimized to completely remove heat due to a steady, uniform heat flux of 500 W cm^?2 imposed over the entire footprint (background heat flux) and a steady, uniform heat flux of 2000 W cm^?2 imposed on the hot spot area only (hot spot heat flux). The two simultaneous objectives are to minimize maximum substrate temperature and minimize pumping power, while keeping the maximum temperature constrained below 85°C and removing all of input thermal energy by convection. The design variables are the inlet average velocity and size of the pin-fins. A response surface is generated for each of the objectives and coupled with a genetic algorithm to arrive at a Pareto frontier of the best trade-off solutions. Numerical results show that, for a specified maximum temperature, optimized arrays with pin-fins having symmetric convex lens shapes create the lowest pressure drop, followed by the symmetric airfoil and circular cross-section pin-fins. An a posteriori three-dimensional stress–deformation analysis incorporating hydrodynamic and thermal loads shows that Von-Mises stress for each pin-fin array is significantly below the yield strength of silicon, thus, confirming structural integrity of such arrays of micro pin-fins.     

A bottom-up estimation of the heating and cooling demand in European industry

Energy balances are usually aggregated at the level of subsector and energy carrier. While heating and cooling accounts for half the energy demand of the European Union’s 28 member states plus Norway, Switzerland and Iceland (EU28 + 3), currently, there are no end-use balances that match Eurostat’s energy balance for the industrial sector. Here, we present a methodology to disaggregate Eurostat’s energy balance for the industrial sector. Doing so, we add the dimensions of temperature level and end-use. The results show that, although a similar distribution of energy use by temperature level can be observed, there are considerable differences among individual countries. These differences are mainly caused by the countries’ heterogeneous economic structures, highlighting that approaches on a process level yield more differentiated results than those based on subsectors only. We calculate the final heating demand of the EU28 + 3 for industrial processes in 2012 to be 1035, 706 and 228 TWh at the respective temperature levels > 500 °C (e.g. iron and steel production), 100–500 °C (e.g. steam use in chemical industry) and < 100 °C (e.g. food industry); 346 TWh is needed for space heating. In addition, 86 TWh is calculated for the industrial process cooling demand for electricity in EU28 + 3. We estimate additional 12 TWh of electricity demand for industrial space cooling. The results presented here have contributed to policy discussions in the EU (European Commision 2016), and we expect the additional level of detail to be relevant when designing policies regarding fuel dependency, fuel switching and specific technologies (e.g. low-temperature heat applications).     

Chemical hot gas cleaning concept for the “CHRISGAS” process

The aim of the CHRISGAS project was the development of a gasification technique to produce clean hydrogen-rich synthesis gas from biomass. In order to improve the process efficiency, this work presents a gas cleaning concept, which combines chemical hot gas cleaning with hot (1 MPa, 900 °C) and warm (1 MPa, 300 °C) filtration. As the focus is set on the removal of H₂S, HCl and KCl, calculations on chemical gas cleaning for the hot and warm gas filter were done using a thermodynamic process model using SimuSage? (GTT-Technologies). The calculations show that Ca-based and Fe-based sorbents are not suitable H₂S sorbents under the conditions of the hot gas filter. For Cu-based sorbents, H₂S concentration below 100 cm³ m^?3 is achievable, if the temperature is reduced below 810 °C. Additional calculations of KCl sorption on alumosilicates under the conditions of the hot gas filter show that the alkali concentration in gasifier-derived gases can be limited to 100 mm³ m^?3. Thus, the condensation temperature of KCl can be decreased down to 580 °C. The results of HCl sorption calculations show that Na- and K-based sorbents are only suitable for temperatures below 600 °C. Therefore, the HCl sorption is transferred to the warm gas filter. The KCl sorption results were confirmed by experiments using bauxite, bentonite, kaolinite and naturally occurring zeolite as sorbents.     

Pre-adsorption of low-grade waste steam for high-temperature steam generation by using composite zeolite and long-term heat storage salt of MgSO4

Adsorptive heat transformer is a promising technology for waster heat recovery and global energy conservation. A novel cyclic adsorption heating system based on direct contact heat exchange method has been established for the purpose of high-temperature steam generation from hot water. Pre-adsorption is originally proposed before generation phase to enhance the system performance with composite zeolite 13X and MgSO₄ in the open-loop adsorption heating system. Composite zeolite is prepared by impregnation method. Experimental results show steam with temperature higher than 200°C is generated from inlet water at 72.0°C. During regeneration phase, dry air at 130°C and relative humidity of 7.37% is employed. Gross temperature lift is 95.0°C to 103°C for different pre-adsorption conditions. The effective steam generation time with pre-adsorption temperature at 90.0°C is prolonged by 27.4%. Meanwhile, the mass of steam is elevated by 16.2% compared with the cycle without pre-adsorption. Exergy coefficient of performance is upgraded by 14.7% and specific heating power for steam generation is increased by 16.0%. The pre-adsorption operation achieved the goal of recovery of low-grade waste steam on adsorbents to enhance the subsequent high-temperature steam generation. After pre-adsorption operation, the packed bed reaches adsorption and thermal equilibrium more quickly during generation phase. Thus, dynamic steam generation is significantly intensified and then system performance is improved correspondingly.     

Quantification of the European industrial heat demand by branch and temperature level

We present the first comprehensive estimate of the final energy demand for heat in all EU28 member states for the reference year 2012, differentiated by temperature levels, comparing two different approaches. Two different calculation approaches based on different data sets yielded estimates of the total final energy demand for heat in the EU28 of 8150 PJ and 8518 PJ in 2012, respectively. Approach 1 distinguishes between three different process heat (PH) temperature levels and results in final energy demand for heat <100°C: 2077 PJ, 100–400°C: 2214 PJ and >400°C: 3859 PJ. The second approach distinguishes between low temperature space heat and hot water (<100°C: 1161 PJ) and four different PH temperature levels with a resulting energy demand of <100°C: 1027 PJ, 100–500°C: 1785 PJ, 500–1000°C: 1679 PJ and >1000°C: 2865 PJ. The high share of high‐temperature heat illustrates the limits to the potential decarbonisation of industrial thermal processes with renewable energy sources such as (non‐concentrating) solar thermal, geothermal or environmental heat. Therefore specific information on required temperature levels is of the essence. This, in turn, points out the relevance of renewable electricity and synthetic fuels based on renewable power for a significant reduction of CO₂ emissions from the industry sector in Europe. Considering current data quality, it is recommended to develop a consistent, comprehensive methodology to significantly improve the data basis on industrial heat demand. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling of a thermal energy storage system based on coupled metal hydrides (magnesium iron – sodium alanate) for concentrating solar power plants

Concentrating solar power plants represent low cost and efficient solutions for renewable electricity production only if adequate thermal energy storage systems are included. Metal hydride thermal energy storage systems have demonstrated the potential to achieve very high volumetric energy densities, high exergetic efficiencies, and low costs. The current work analyzes the technical feasibility and the performance of a storage system based on the high temperature Mg₂FeH₆ hydride coupled with the low temperature Na₃AlH₆ hydride. To accomplish this, a detailed transport model has been set up and the coupled metal hydride system has been simulated based on a laboratory scale experimental configuration. Proper kinetics expressions have been developed and included in the model to replicate the absorption and desorption process in the high temperature and low temperature hydride materials. The system showed adequate hydrogen transfer between the two metal hydrides, with almost complete charging and discharging, during both thermal energy storage and thermal energy release. The system operating temperatures varied from 450 °C to 500 °C, with hydrogen pressures between 30 bar and 70 bar. This makes the thermal energy storage system a suitable candidate for pairing with a solar driven steam power plant. The model results, obtained for the selected experimental configuration, showed an actual thermal energy storage system volumetric energy density of about 132 kWh/m³, which is more than 5 times the U.S. Department of Energy SunShot target (25 kWh/m³).     

Syngas production by non-catalytic reforming of biogas with steam addition under filtration combustion mode

Biogas conversion to syngas (mainly H₂ and CO) is considered an upgrade method that yields a fuel with a higher energy density. Studies on syngas production were conducted on an inert porous media reactor under a filtration combustion mode of biogas with steam addition, as a non-catalytic method for biogas valorization. The reactor was operated under a constant filtration velocity of 34.4 cm/s, equivalence ratio of 2.0, and biogas concentration of 60 vol% Natural Gas/40 vol% CO₂, while the steam to carbon ratio (S/C) was varied between 0.0 and 2.0. Total volumetric flow remained constant at 7 L/min. Combustion wave temperature and propagation rate, product gas composition, reactants conversion as well as H₂ and CO selectivity were measured as a function of S/C ratio. Chromatographic parameters, method validation and measurement uncertainty were developed and optimized. It was observed that S/C ratio of 2.0 gave optimal results under studied conditions for biogas conversion, leading to maximum concentrations of 10.34 vol% H₂, 9.98 vol% CO and highest thermal efficiency of 64.2% associated with a modified EROI of 46.3%, which considered energy consumption for steam supply. Conclusions indicated that the increment of the steam co-fed with the reactants favored the non-catalytic conversion of biogas and thus resulted in an effective fuel upgrading.     

Steam reforming and oxidative steam reforming for hydrogen production from bioethanol over Mg2AlNiXHZOY nano-oxyhydride catalysts

Mg₂AlNi_XH_ZO_Y nano-oxyhydrides formation is evidenced during pre-treatment in H₂ at 450 °C of Mg₂AlNi_XO_Y nano-compounds leading to highly performant catalysts in ethanol conversion and H₂ formation, particularly at low temperature, through catalytic steam reforming (SRE) and oxidative steam reforming (OSRE). Total conversion of ethanol is obtained in SRE and OSRE with high stability. A higher production of H₂ (60 L h^?1 g_cat^?1) can be achieved at a reaction temperature of 300 °C in OSRE conditions compared to SRE (10 L h^?1 g_cat^?1) mainly because of a beneficial use of a high concentration of ethanol (14 mol%) in presence of O₂. Moreover, carbon formation is decreased and a much lower input of energy of 50 °C is used to get a temperature of 300 °C when O₂ is added. Different physico-chemical characterizations and in particular in H₂ (TPR, H₂-XRD, INS) and after tests allow to conclude that the presence of Ni²⁺ cations in strong interaction with other cations, anionic vacancies and hydride species on and inside the solid play an important role in the catalytic performance (conversion and selectivity) and stability.     

Experimental Study of Deposits Removal in Thermal Desalination Plants by the Thermal Shock Technique

Deposition of salts on heat transfer surfaces in thermal desalination plants can lead to operational failure. Scale removal can occur by applying a thermal shock, which is a sudden decrease in the heating process. The difference in thermal expansion between the heat transfer surface and the deposit layer plays a key role in the thermal shock process. The objective of this research is to determine experimentally the minimum temperature of the heating surface in desalination units, such that the thermal shock is still applicable. The minimum heating temperature is important for minimization of heat losses. An experimental setup has been designed and developed, and it consists of an oil tank in which oil is heated by electrical heaters. The heated oil is circulated by a gear pump to the steam generator, which contains the water to be desalinated, that is, a CaSO₄ solution, at atmospheric pressure. The water is heated and converted into steam by the hot oil leaving the salts behind, that is, the fouling layer, on the tubes of the steam generator. A thermal shock is applied when the asymptotic behavior is approached, such that the flow of the hot oil is suddenly stopped for a short period of time before resuming it again. The minimum heating temperature has been determined for two types of tubes: stainless steel and copper, and at a salt concentration of 2 g/L. The minimum heating oil temperature that allows the applicability of the thermal shock is 130°C when using copper tubes, and 140°C for stainless-steel tubes.     

Improved heating floor thermal performance by adding PCM microcapsules enhanced by single and hybrid nanoparticles

A heating floor is a low-temperature emitter consisting of pipelines in which a fluid circulates between 35°C and 45°C. To ensure energy efficiency, occupant comfort, and building material durability, proper heat management is crucial in buildings. By using phase change materials (PCMs) in building envelopes, the indoor temperature can be regulated through the storage and release of thermal energy, which reduces energy consumption and enhances occupant comfort. In this study, we evaluated numerically a heating floor that incorporates a PCM enhanced by nanoparticles (NePCM). The aim of the numerical analysis is to assess the impact of the addition of single and hybrid nanoparticles in different proportions to the PCM layer on the thermal performance of the PCM-based floor. Therefore, two main objectives are defined. The primary is to take advantage of the storage capacity of a PCM layer by integrating it into the ground; second, to evaluate the hot water temperature levels effect on the floor's performance. Additionally, we address the low thermal conductivity of PCM by enhancing PCM microcapsules with single and hybrid nanoparticles and comparing them to pure PCM. The numerical results obtained show that positioning the PCM microcapsules above the heating tubes (upper position) provides an optimum improvement in thermal performance. Moreover, the addition of hybrid nanoparticles within the base PCM, 1% of Cu mixed with 4% of Al₂O₃, allows an increase of 4°C, which relates to a reduction of 18% in the internal temperature amplitude and a phase shift of 6 h 30 min compared with the conventional heated floor in which there is no PCM.     

Hydrogen production from oil sludge gasification/biomass mixtures and potential use in hydrotreatment processes

Gasification of oil sludge (OS) from crude oil refinery and biomass was investigated to evaluate hydrogen production and its potential use in diesel oil hydrodesulphurization process. Gasification process was studied by Aspen Hysys^® tools, considering different kinetic model for main OS compounds. Air and superheated steam mixtures as gasifying agents were simulated. Gasification parameters like: temperature, syngas chemical composition and gas yield were evaluated. Results showed OS thermal conversion needs a working temperature above 1300 °C to ensure a high conversion (>90%) of OS compounds. Thermal energy requirement for gasification was estimated between 0.80 and 1.25 kWh/kg OS, considering equivalence air (ER) and steam/oil sludge (SOS) ratio between 0.25-0.37 and 0.2–1.5 kg steam/kg OS, respectively. The gas yield was 2.28 Nm³/kg OS, with a H₂ content close to 25 mol%, for a H₂ potential production about 1.84 Nm³ H₂/kg OS; nevertheless, when OS and biomass mixtures are used, hydrogen production increases to 3.51 Nm³ H₂/kg OS, meaning 37% of H₂ (from natural gas) required for diesel oil hydrodesulphurization could be replaced, becoming an added value technological alternative for OS waste conversion as a source of H₂, inducing a considerable reduction of greenhouse gases and non-renewables resources.     

Performance analysis and validation on transportation of heat energy over long distance by ammonia–water absorption cycle

This paper presents the thermodynamic and hydrodynamic feasibility of the application of the ammonia–water absorption system for heat or cold transportation over long distance. A model of a long‐distance heat energy transportation system is built and analyzed, and it shows satisfactory and attractive results. When a steam heat source at the temperature of 120°C is available, the user site can get hot water output at about 55°C with the thermal COP of about 0.6 and the electric COP of about 100 in winter, and cold water output at about 8°C with the thermal COP of about 0.5 and the electric COP of 50 in summer. A small‐size prototype is built to verify the performance analysis. Basically the experimental data show good accordance with the analysis results. The ammonia–water absorption system is a potential prospective solution for the heat or cold transportation over long distance. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance of active nickel loaded lignite char catalyst on conversion of coffee residue into rich-synthesis gas by gasification

Performance of nickel-loaded lignite char catalyst on conversion of coffee residue into synthesis gas by catalytic steam gasification was carried out at low reaction temperatures ranging from 500 °C to 650 °C in the two-stage quartz fixed bed reactor. The effects of steam pressures (30, 36 and 50 kPa corresponding to S/B = 2.23, 2.92 5.16, respectively) and catalyst to biomass ratios (C/B ratio = 0, 1, 3) were considered. Nickel-loaded lignite char was prepared as a catalyst with a low nickel loading amount of 12.9 wt%. The gas yields in the catalytic steam gasification process strongly depended on the reaction temperature and C/B ratio. The total gas yields obtained in catalytic steam gasification was higher than that of catalytic pyrolysis, steam gasification and non-catalytic pyrolysis with steam absence by factors of 3.0, 3.8 and 7.7, respectively. To produce the high synthesis gas, it could be taken at 600 °C with total gas yields of 67.13 and 127.18 mmol/g biomass-d.a.f. for C/B ratios of 1.0 and 3.0, respectively. However, the maximum H₂/CO ratio was 3.57 at a reaction temperature of 600 °C, S/B of 2.23 and C/B of 1.0. Considering the conversion of coffee residue by catalytic steam gasification using the nickel-loaded lignite char catalyst, it is possible to covert the coffee residue volatiles into rich synthesis gas.     

Kinetic characteristics of in-situ char-steam gasification following pyrolysis of a demineralized coal

This study aims to examine the char-steam reactions in-situ, following the pyrolysis process of a demineralized coal in a micro fluidized bed reactor, with particular focuses on gas release and its kinetics characteristics. The main experimental variables were temperatures (925 °C?1075 °C) and steam concentrations (15%–35% H₂O), and the combination of pyrolysis and subsequent gasification in one experiment was achieved switching the atmosphere from pure argon to steam and argon mixture. The results indicate that when temperature was higher than 975 °C, the absolute carbon conversion rate during the char gasification could easily reach 100%. When temperature was 1025 °C and 1075 °C, the carbon conversion rate changed little with steam concentration increasing from 25% to 35%. The activation energy calculated from shrinking core model and random pore model was all between 186 and 194 kJ/mol, and the fitting accuracy of shrinking core model was higher than that of the random pore model in this study. The char reactivity from demineralized coal pyrolysis gradually worsened with decreasing temperature and steam partial pressure. The range of reaction order of steam gasification was 0.49–0.61. Compared to raw coal, the progress of water gas shift reaction (CO + H₂O ? CO₂ + H₂) was hindered during the steam gasification of char obtained from the demineralized coal pyrolysis. Meanwhile, the gas content from the char gasification after the demineralized coal pyrolysis showed a low sensitivity to the change in temperature.